Key cutting machines, also commonly called duplicating machines, are well known. A known type of such machines comprises a base on which a feeler is mounted to mechanically sense the notches of the notching pattern of an original key to be duplicated, together with a milling cutter to form similar notches on a blank key to be cut.
On the same base a movable structure is also mounted supporting two clamps, to which the original key to be duplicated and the blank key to be cut are fixed. The arrangement of the parts is such that the two keys are disposed with the axes of their respective shanks parallel and that when the original key faces the feeler the blank key faces the cutter.
In this manner, by moving the movable structure such that the feeler slides along the pattern notches of the original key the cutter forms, on the blank key, notches which are substantially identical to those of the original key in terms of position and depth.
In another known type of duplicating machine the movement of the blank key to be cut relative to the cutter is obtained mechanically on the basis of notching pattern data contained in a database. In this case, cutting the blank key does not require the physical presence of the original key as the notching data can be read off at a prior moment by a device separate from the duplicating machine, or can be made available via a previously memorized notching code.
In all cases the blank key to be cut must at least be retained by a clamp in a position in front of a milling cutter and is moved relative to said cutter such that this forms in the key edge the notches corresponding to the notching pattern to be provided.
Known clamps generally comprise two jaws, between which the concerned key is clamped. These jaws are mounted on a generally vertical pin and are maintained spaced apart by a spring. The pin has its upper portion threaded and on this a knob is screwed, which when operated by the operator causes the two jaws to move towards each other and clamp the interposed key.
A drawback of known clamps of this type is that if the knob is too loosely tightened the key does not become securely fixed and can vibrate during milling, such that in some cases it can even become detached from the clamp. These is hence a risk of cutter breakage and in any event an imperfect notching result. If instead the knob is too tightly tightened, the clamp can undergo early wear and the key be damaged, especially if made of soft material such asaluminum.
To illustrate, U.S. Pat. No. 4,709,511, granted Dec. 1, 1987, discloses a clamp for duplicating machines for keys. The clamp includes a vertically extending pin (4) with a threaded upper end, a pair of jaws (1, 2) mounted on the pin, and supported on a support carriage (3), as shown in FIG. 1. A spring (6,8) or other resilient member normally biases, or spaces, the jaws apart so that a key may be positioned therebetween. Rotation of a handgrip (10) about the threaded upper of pin (4) overcomes the bias of the spring, and applies a clamping force to the key to retain same in fixed position in the slot formed between the jaws. A rib (12), or similar projection, is defined on the lower jaw, to provide a lever-like force that prevents the jaws from sticking together during the clamping phase, and overcomes difficulties in opening the jaws during the release phase of the cycle of operation.
U.S. Pat. No. 6,641,339, granted Nov. 4, 2003, discloses another clamp for a key duplicating machine. The clamp includes a pair of jaws (10,12) mounted on a vertically extending pin (6); the jaws are supported by base (2), which encircles the lower end of the pin. The jaws are normally biased apart by a coil spring or other resilient member, so that a key (14) may be inserted into the gap between the jaws. The jaws are mounted on the pin, and the upper end of the pin is threaded into engagement with handgrip (16). The handgrip, or knob, is screwed into the upper end of pin (6) to lock key (14), and jaws (10,12) to the base (2). A gauge (20) is operatively associated with the seat to define a proper position for the key.
Therefore, the prior art discloses clamps for key cutting machines, in which the clamping force delivered to the jaws, to maintain the keys in fixed position, was fixed in magnitude. The need for a clamp for key cutting machines, in which a constant key clamping force may be applied without the risk of damaging the key and/or the milling cutter, remains unsatisfied.